1. Field of the Invention
The present invention relates to a gate of a mold for an injection molding machine wherein a molding compound is kept in a molten form in an inner passage and a molded product is ejected in a solidified or hardened form (hereinafter referred to as a runnerless mold).
2. Description of the Prior Art
In a hot runner molding method, a molten resin melted in an injection molding machine in a plastic form is fed into a hot runner of a mold kept at high temperature so as to keep the molding compound remaining in the runner part in a molten form, and the molten molding compound is injected at high velocity under high pressure through a gate at the end of the hot runner into a cavity of the cool mold, and the molded product is cooled and ejected. This method is advantageous from the viewpoint of labour saving and reduction of material loss because it is a runnerless molding. On the other hand, when a molding compound having a low melt flow viscosity is molded, leakage or threading of the melt is caused which prevents the automatic molding and renders damaged products.
Studies have been made to overcome these disadvantages by providing a valve mechanism in the hot runner to open the valve of the mechanism at the injection of the molten molding compound and to close the valve at the end of the injection. However, the conventional valve mechanism has a cylinder-piston structure for the guide in the opening and closing operation of the valve whereby the molten resin is easily immersed into the sliding gap causing troubles. Moreover, the disadvantage is the complicated structure and high production cost.